(https://resources.stuff.co.nz/content/dam/images/1/f/z/x/g/q/image.related.StuffLandscapeSixteenByNine.710x400.1fzzb4.png/1487200006154.jpg)
Name: Ihaka Arahanga
Birthdate: June 28, 1985; 27 years old
Birthplace: Kakanui, New Zealand
Ihaka is Kaia's fraternal twin brother! Like her, he grew up on New Zealand's South Island, spending most of his childhood outside of Oamaru. The twins' mother, who was a magical researcher at the University of New Zealand, disappeared when they were young. Unlike Kaia, who followed in her mother's footsteps and went on to study astrophysics, Ihaka took after their (Squib) father and became an apprentice beast handler.
He became an Animagus when he was eighteen alongside his twin sister, but his animal form is open! (Perhaps a kaka (https://en.wikipedia.org/wiki/Kākā) to match her kea form, or something completely different?)
Check out Kaia's biography (https://absitomen.com/index.php?topic=20054) for more background on their family history.
Ihaka's personality is open: he could be laid back and relaxed like Kaia, or more driven, or mischievous, or whatever you'd like. His magizoology specialty and the reason why he might come to the UK is also open. Maybe he's a dragon researcher and has gotten a new job with the British Ministry? Maybe he's working for the Werewolf Capture Unit? Maybe he's found out something about why their mother disappeared and moved to London to investigate?
Face claim is also open, but he should be a Maori male that looks like he's in his mid-late twenties. Some suggestions are James Rolleston (pictured above), Pana Hema Taylor, or Matariki Whatarau.